The present invention relates to an oil free screw compressor which synchronously rotates a pair of screw rotors without being in contact, and more particularly to an oil free screw compressor preferable for being driven by a high speed motor.
A conventional oil free screw compressor is, for example, as described in Japanese Patent Unexamined Publication No. 6-346881, structured such as to increase a rotational speed of a motor by using a belt and a gear so as to rotate a screw compressor main body. Further, in Japanese Patent Unexamined Publication No. 3-151592, there is described an embodiment of connecting a speed increasing gear apparatus receiving a speed increasing gear within a casing to a rotor shaft having a screw gear formed thereon via a coupling.
In this case, in the screw compressor, in addition to an operation control such as a load, an unload and the like, a capacity control for controlling an opening and closing operation of a suction throttling valve in accordance with a consumption requirement in the demand side is performed. As an example of the capacity control, there is described in Japanese Patent Unexamined Publication No. 59-93989 a structure in which a valve plate for the suction throttling valve is mounted to a front end of an air cylinder operated by a pressure of the compressor itself and an amount of a suction air is adjusted at two stages by moving the valve plate.
Here, the compressor described in Japanese Patent Unexamined Publication No. 6-346881 mentioned above requires a lot of parts such as a bearing for rotating and supporting a speed increasing gear, a rotary shaft for mounting the speed increasing gear, a belt and a pulley for transmitting a power having an increased speed and the like in addition to a gear case for receiving the speed increasing gear, thereby causing an increase of a cost for the compressor. Further, in this compressor, an electric motor for driving the screw rotor is enlarged, and accordingly, the compressor is insufficient in view of making small-sized a whole of the compressor unit including a stand for fixing the electric motor.
Further, in the compressor described in Japanese Patent Unexamined Publication No. 3-151592, since the speed increase is not performed by the belt, a speed increasing rate in the speed increasing gear is increased, and a gear case for receiving the speed increasing gear is enlarged. Then, in order to make the compressor as series of widely used compressors, it is necessary to combine various kinds of compressor main bodies and speed increasing gear apparatuses, thereby causing an increase of a cost in view of preparing various kinds of compressors.
Still further, in the compressor described in Japanese Patent Unexamined Publication No. 59-93989, since an air for operating a suction throttling valve is supplied to an air cylinder at every time when a line pressure is changed, a three-way electromagnetic valve is connected to an air cylinder and a supply hole for the operating air in the air cylinder is switched by the three-way electromagnetic valve. As mentioned above, since it is necessary to provide with the three-way electromagnetic valve, a structure of a flow rate control system becomes complex as well as the compressor becomes expensive. Further, in order to cancel an unloading at a time of start, a plurality of three-way electromagnetic valves are required, so that a structure of a capacity control apparatus becomes complex. In any one of the compressors mentioned above, a certain degree of consideration is given to making the compressor compact, however, a more compact structure is desired.
The present invention is made in view of the problems mentioned above in the conventional arts, and an object of the present invention is to make a structure of a compressor unit simple. Another object of the present invention is to making a compressor unit compact so as to realize a compressor unit having a great freedom for placing. The other object of the present invention is to realize an inexpensive compressor unit having a reduced cost. The other object of the present invention is to make elements in a side of a compressor main body common with elements in a side of an electric motor so as to realize a compressor unit having a high reliability.
In order to achieve the objects mentioned above, in accordance with the present invention, there is provided an oil free screw compressor comprising a motor shaft to which a motor rotor is mounted, a motor casing for holding a motor stator arranged in opposite to the motor rotor, a male rotor in which a screw-like male tooth shape is formed, a female rotor in which a screw-like female tooth shape is formed, and a casing for receiving the male rotor and the female rotor. In the above structure, a first feature is that a rotational speed of the motor is made equal to a rotational speed of at least one of the male rotor and the female rotor.
In this structure, the rotational shaft formed in any one of the male rotor and the female rotor and the motor shaft may be an integral rotary shaft. Further, the structure may be made such that a first gear is provided in a side of one end of any one of the male rotor and the female rotor, a second gear meshing with the first gear is provided in a side of one end of the motor shaft, and a ratio of a number of teeth between the first gear and the second gear may be set to be substantially one to one.
In order to achieve the objects mentioned above, a second feature of the present invention is that a rotational speed of a high frequency electric motor is made equal to a rotational speed of at least one of the male rotor and the female rotor.
Preferably, the structure is made such that a first gear is provided in a side of one end of any one of the male rotor and the female rotor, a second gear meshing with the first gear is provided in a side of one end of the high frequency electric motor, and a ratio of a number of teeth between the first gear and the second gear is set to be one to one. Further, the structure is preferably made such that a roller bearing for rotatably supporting the male rotor and the female rotor is provided in each of the rotors, and a roller bearing having the same size as that of the roller bearing is provided in the high frequency electric motor. More preferably, the structure is made such that a screw seal for sealing a lubricating oil supplied to the roller bearing for supporting the male rotor and the female rotor is provided in each of the rotors, a screw seal for sealing a lubricating oil supplied to the roller bearing provided in the high frequency electric motor is provided, and sizes of the screw seals are made equal to each other.
In order to achieve the objects mentioned above, a third feature of the present invention is that a high speed motor driven by a high frequency inverter is connected to a suction side of the compressor main body, the high speed motor has a motor shaft in which the motor rotor is formed, a third bearing for rotating and supporting the motor shaft and a second shaft sealing apparatus for preventing a lubricating oil for lubricating the third bearing from entering within the high speed motor, the first, second and third bearings are made the same with respect to each other, and the first shaft sealing apparatus and the second shaft sealing apparatus are made the same.
It is desirable to fit the first gear to the shaft end of the rotor, fit the second gear meshing with the first gear to the shaft end of the high speed motor in a load side, and to set the ratio of the number of the teeth between the first and second gears to a range from two to one to one to two. Further, it is desirable to directly connect the shaft end of the male rotor provided in the compressor main body to the shaft end in the load side of the high speed motor by means of a coupling or a spline. Further, it is desirable to provide with bearings supporting the male rotor and positioned at both end portions of the rotor, a motor rotor positioned between one of the bearings and a gear groove portion of the male rotor and fitted to the male rotor, a motor stator opposing to the motor rotor and a motor casing for holding the motor stator, and connect the motor casing to the suction side of the casing.
More preferably, the structure is made such that the compressor main body and the high speed motor are integrally formed, a common table which receives an after cooler for cooling a compressed air compressed in the compressor main body, a pre-cooler and an oil cooler for cooling a lubricating oil is provided, and the integrated compressor main body and high speed motor are arranged above the common table. Further, the structure may be made such that an air cooler for cooling an operating air compressed in the compressor main body is provided in a downstream side of the compressor main body, a check valve is provided in a further downstream portion of the air cooler, an air discharging pipe passage diverging from an upstream side of the check valve and having an air discharging cooler and an aid discharging valve is provided, and an air discharging valve control apparatus which closes the air discharging valve at a time of starting the compressor main body and operating it under no load and opens the air discharging valve at a time of operating it under a load is provided.
Accordingly, the following effects can be obtained.
(1) A speed increasing apparatus such as a speed increasing gear, a belt and the like is not required, so that it is possible to make the oil free screw compressor unit compact, light and inexpensive.
(2) A capacity control apparatus for the suction throttling valve, the three way electromagnetic valve and the like is not required, so that it is possible to make the structure of the oil free screw compressor unit simple and inexpensive.
(3) Since it is possible to employ the rotating system conventionally having a high reliability to the electric motor system and the compressor main body system by making an oscillation mechanical structure common between the electric motor system and the compressor main body system, it is possible to provide an oil free screw compressor unit capable of stably rotating to a high speed range.
(4) It is possible to make the oil free screw compressor inexpensive and improve a reliability by making parts common between the electric motor system and the compressor main body system.